1. Field of the Invention
This invention relates to a flat type stepping motor and more particularly to a flat ultra thin type floppy disk which is suited for rotationally driving an ultra small size floppy disk.
2. Related Art Statement
As the stepping motor having a hybrid type rotor employed in the prior art, the construction shown in FIG. 2 has been most typical, although the title of the literature is not shown herein specifically.
Referring to FIG. 2, the reference numeral 1 denotes a casing having a front cap 2 and a rear cap 3. Between these caps, there is provided a stator 6 consisting essentially of a stator core 4 and a winding 5.
The stator 6 in the form of a ring in a plan view is formed by a plurality of teeth and a winding provided in the inside of the casing 1.
A pair of bearing holding units 7, 8 are provided at either end along the center axis of the casing 1, these units holding a first bearing unit 9 and a second bearing unit 10, respectively. A corrugated washer 11 is disposed between the second bearing unit 10 and the rear cap 3.
A rotary shaft 12 is mounted for rotation by the bearing units 9 and 10. The one end of the rotary shaft 12 is passed through and extended outwardly of a through-hole 7a in the bearing holding unit 7.
At about the center of the rotary shaft 12 are mounted first and second rotor yokes 13, 14 formed as disks, while a ring-like magnet 15 is clamped between these rotor yokes 13 and 14. A rotor generally indicated at 16 is made up of the rotor yokes 13, 14 and the magnet 15.
A first spacer 17 is arranged between the first bearing unit 9 and the first rotor yoke 13 while a second spacer 18 is provided between the second rotor yoke 14 and the second bearing unit 10.
The above described conventional flat type stepping motor operates in such a manner that, in the state of FIG. 2, drive pulses are applied to the winding 5 provided to the stator 6, so that the rotor 16, magnetized to a plurality of magnetic poles, is driven in a stepwise rotation by a predetermined angle each time the driving pulse is applied.
In the above described construction of the conventional stepping motor, since the rotor 16 is sandwiched between the pair of spacers 17 and 18, it has been extremely difficult to reduce the axial thickness so as to provide a flat type motor. Thus the lower limit of the motor thickness of approximately 10 mm cannot be exceeded by reducing the size of the component parts.
On the other hand, 8-inch size floppy disks are now being used in the word processor applications in preference to the 5-inch size floppy disks. The prospect is that 2-inch and 1-inch size floppy disks will be offered to the market in the near future. In association therewith, it is demanded that a stepping motor with a thickness of 7 mm be developed in place of the currently used version with a thickness of 10 mm. Such a demand cannot be fulfilled with the aforementioned prior-art construction of the stepping motor.